1. Technical Field
The embodiments described herein relate to semiconductor integrated circuits, and in particular, to apparatus and methods for a test control circuit and a reference voltage generating circuit having the same.
2. Related Art
A conventional semiconductor integrated circuit includes internal voltage generating circuits that generate various kinds of internal voltages, of various voltage levels from a relatively high voltage, external power supply. Conventional semiconductor integrated circuits are fabricated via a series of manufacturing processes and are tested for normal operation before the device is shipped. For example, a conventional semiconductor integrated circuit can be subject to an internal voltage trimming test. An internal voltage trimming test determines whether an internal voltage is outside of a prescribed voltage range, e.g., due to manufacturing tolerances or changes in manufacturing processes, and when the internal voltage is out of the prescribed voltage range, then trims the internal voltage such that the internal voltage falls within the prescribed voltage range. A conventional internal voltage trimming test can determine the optimum internal voltage for the semiconductor integrated circuit and control an internal voltage generating circuit of the semiconductor integrated circuit to control the level of the internal voltage so as to achieve the optimum voltage level.
FIG. 1 is a timing diagram illustrating the operation of a conventional test control circuit. As can be seen, a conventional test control circuit receives a pulsed voltage trimming test signal (Trimming_Test), and outputs a 15-bit trimming signal (TRIM<0:15>). Each bit of the 15-bit trimming signal (TRIM<0:15>) can be viewed as an individual signal (TRM<0>), TRM<1>), . . . (TRM<14>). In this example, before the test starts, the seventh trimming signal (TRIM<7>) is at a high voltage level, and the other trimming signals (TRIM<0:6>) and (TRIM<8:15>) are all at a low voltage level. Each time the voltage trimming test signal (Trimming_Test) is received, one of the trimming signals TRIM<0:15> goes high, and the other trimming signals go, or remain low.
Referring to FIG. 1, it can be seen that, each time the voltage trimming test signal (Trimming_Test) is received, the sixth, fifth, fourth trimming signals (TRIM<6>), (TRIM<5>), (TRIM<4>), etc., sequentially go high, and after the zero-th trimming signal (TRIM<0>) goes high, the eighth, ninth, tenth trimming signals, (TRIM<8>);(TRIM<9>);(TRIM<10>), etc., go high sequentially.
Accordingly, a conventional test control circuit can generate a reference voltage based on the trimming signals TRIM<0:15>, and can determine the optimum reference voltage condition for the internal circuit using the reference voltage.
As shown in FIG. 1, during a conventional voltage trimming test, a voltage is supplied from the outside. If the voltage to be supplied from the outside (hereinafter, referred to as ‘external voltage’) is higher than the voltage of the internal circuit, no problems occur. However, if the external voltage is lower than the potential of the internal circuit, a current may flow from the internal circuit to a pad to which the external voltage is supplied. Therefore, it is necessary to implement a circuit that can perform a normal voltage trimming test when the external voltage is lower than that of the circuit being tested.